The proliferation and popularity of mobile radio and telephony applications has led to market demand for communication systems with low cost, low power, and small form-factor radio-frequency (RF) transceivers. As a result, recent research has focused on providing monolithic transceivers using low-cost complementary metal-oxide semiconductor (CMOS) technology. One aspect of research efforts has focused on providing an RF transceiver within a single integrated circuit (IC). The integration of transceiver circuits is not a trivial problem, as it must take into account the requirements of the transceiver's circuitry and the communication standards governing the transceiver's operation.
From the perspective of the transceiver's circuitry, RF transceivers typically include sensitive components susceptible to noise and interference with one another and with external sources. Integrating the transceiver's circuitry into one integrated circuit may exacerbate interference among the various blocks of the transceiver's circuitry. Moreover, communication standards governing RF transceiver operation outline a set of requirements for noise, inter-modulation, blocking performance, output power, and spectral emission of the transceiver. Unfortunately, no technique for addressing all of the above issues in high-performance RF receivers or transceivers, for example, RF transceivers used in cellular and telephony applications, has been developed. A need therefore exists for techniques of partitioning and integrating RF receivers or transceivers that would provide low-cost, low form-factor RF transceivers for high-performance applications, for example, in cellular handsets.
A further aspect of RF apparatus, such as RF transceivers, receivers, and transmitters, relates to providing local oscillator (LO) signals. Typical RF apparatus employ LO circuitry that generates and supplies LO signals. The RF apparatus use LO signals in the receive-path circuitry and/or in the transmit-path circuitry. Consequently, the stability of the LO signal impacts the performance of the RF apparatus. Conventional LO circuitry suffer from variations in the output power of the LO output signals. The variations result, for example, from semiconductor manufacturing process variations and temperature changes. Regardless of the source, the variations in the output power of the LO output signals degrades the performance of the LO circuitry and, consequently, the performance of the RF circuitry. A need therefore exists for LO circuitry that provides a relatively constant output power over physical variations, such as process and temperature variations.